Hi Richard, ?if ?ifelse ?subset ?[
depending on the specific operation. See inline. Given a data frame tdf with x, y, and a (or with vectors creating a data frame using): tdf <- data.frame(x=x, y=y, a=a) On Sat, Mar 22, 2014 at 10:21 PM, Richard Sherman <rss....@gmail.com> wrote: > Hi all, > > A simple question, new-ish to R, coming from Stata, and I yes I've looked at > great length and not found ... > > In Stata I might write (with * in place of #) > > # regress y on x in the set of observations where a==1 > reg y x if a==1 lm(y ~ x, data=subset(tdf, a==1)) > > # descriptives on x where a==1 > su x if a==1 summary(subset(tdf, a==1)$x) or summary(tdf[tdf$a == 1,]) or if they are vectors summary(x[a==1]) > > # generate a logical depending on the value of a variable > gen z = (a == 1) z <- a==1 > > # or likewise for a numeric > gen x = y if a == 1 I'm not sure what this one is supposed to do. What's x if a isn't 1? But those examples should be enough to get you started, especially if you also read the Intro to R that comes with your R installation. Subsetting is a very basic operation, as you say, and pretty much every intro/tutorial I've read talks about it. I'm not sure where you looked in your extensive searching. Sarah > > # show the values of a variable based on the value of another variable > di y if a ~= . > > # generate a logical based on missing-ness of a variable > gen w = (a~=.) > > or any of many similar operations conditional on the value of a variable. > > Believe it or not this is a big obstacle to learning R. > > --- > Richard Sherman -- Sarah Goslee http://www.functionaldiversity.org ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.